SUBMITTED BY:

RAVI NARAIAN PANDEY.

Decorating whether for aesthetic purposes. (e.g. to improve resistance to wear, scratching, marring, light or heat etc.) is frequently required in the manufacture of articles from any plastic, whether thermoplastic or thermo set. Each presents its own characteristics and hence its own problems; thus we caution the reader to investigate the various techniques and their applicability to the particular plastic that is involved in any given job.

1. Determine the decorating technique that best suits the desired end effect.

2.Make sure that the plastic being used is suitable for the technique selected. The choice can have a significant effect on the entire finishing line. Some plastics, like the polyolefin's and acetals, for example, may require pretreatment. These pretreatment systems ideally should be hooked into the production line-either just prior to decorating or just after molding.

Be certain that the design of the product does not place any limitations on the successful decoration of the part.

Good product design is a key to case of decorating and for keeping costs in line.

Reinforcing ribs, marks, caused by welding knitting of the material as it enters as it enters the mold, and even knock-out pin marks may show through, and cause poor adhesion of the coating or other decorative surface to the part, or otherwise interfere with the method of decoration.

If this is the case, the part may have to be redesigned, or post-finishing operations such as sanding may be required.

Painting on plastics. Printing on plastics.Vacuum Metallizing Surface treatment Integral Coloring

Buy the best tools and equipment you can afford, especially paint brushes.

Buy good quality paint and materials. Buying cheap paint is often a false economy as many more coats are usually required.

Follow the manufacturers instructions on tins and other materials. don't always interpret too literally as there is usually a degree of flexibility, especially in diluting paints.

Try to ensure that you have bought enough materials to complete the job. This is essential when buying wall-paper.

ROUGH GUIDE TO USING MATERIALS

Fillers come in two categories; ready to use and those you mix yourself.

The only one that you would normally mix yourself is filler bought in powder form that you mix with water to form a paste.

It is cheaper to mix this kind of filler yourself than to buy it ready-mixed. This kind of filler, e.g. Polyfill, is used to repair cracks in plaster, holes and other general repairs.

Linseed oil Putty is only used to repair and fill holes in wood, glazing around wooden and metal frames and windows.

Brummer or wood filler is used to repair holes in wood and dries rock hard so apply it as smoothly as possible.

Primers are used to apply first coat to bare wood and metal. For galvanized metal a special zinc primer must be used otherwise your subsequent coats will eventually flake off.

Sealers are used for preserving, waterproofing and preventing problems occurring to subsequent coats caused by chemicals and fungi seeping through from the underlying surface. Many different sealers are used to counteract different problems.

Undercoats/basecoats provide the surface for the following finish coat.

This is by far the most important stage in getting a first class finish.

If necessary a second or even third undercoat should be applied if needed.

Gloss, semi-gloss, eggshell and matt are the usual type of finishes used; a high-gloss finish being far the most common.

It is often difficult to get an undercoat to match various stronger colours and manufacturers normally recommend two coats of finish.

These are paints, (which are water-based) for use on ceilings and walls.

They are easy to use and dry quickly. They can be used on interior wood but lack

the hard-wearing qualities of undercoat and gloss.

A very important part of decorating is preparing the surfaces to be painted.

Sandpaper is the most commonly used material for rubbing-down.

Sanding pads are useful too. Lots of materials can be used, e.g. Pumice

stone.

The two most common thinners used are water for emulsions/latex and Turpentine Substitute

or White Spirit( for solvent based paints).

Special spirit thinners are needed for cellulose paints.

Just as with metal or wood, getting a tightly adhering coating depends on more than mere good luck.

It requires carefully matching the paint system and the plastic, plus close attention to the nature of the plastic.

Some of the guidelines to be followed are listed below and recommended paints for the various plastics are given in this table:

PlasticPlastic Coat ability Coat ability Pretreatment Pretreatment Recommended coating Recommended coating typestypes

ABSABS GoodGood SolventSolvent Vinyl, modified vinyl, Vinyl, modified vinyl, polyurethane, acrylic. polyurethane, acrylic.

AcrylicAcrylic GoodGood Solvent wipeSolvent wipe Acrylic, vinyl, Acrylic, vinyl, nitrocellulose nitrocellulose

Cellulose Cellulose acetate and acetate and butyrate butyrate

GoodGood Solvent wipeSolvent wipe Acrylic, vinyl, Acrylic, vinyl, polyurethane polyurethane

Phenolic and Phenolic and melaminemelamine

DifficultDifficult Solvent wipeSolvent wipe Alkyds, polyurethane, Alkyds, polyurethane, epoxy, acrylicepoxy, acrylic

PolycarbonatePolycarbonate FairFair PrimerPrimer Polyurethane, acrylic, Polyurethane, acrylic, modified acrylic.modified acrylic.

Polyester Polyester GoodGood Solvent wipe Solvent wipe Polyurethane, epoxyPolyurethane, epoxy

PolyolefinsPolyolefins DifficultDifficult Flame solvent Flame solvent or primeror primer

Polyurethane, Polyurethane, nitrocellulose, modified nitrocellulose, modified acrylic. acrylic.

Polyurethane Polyurethane oxide-basedoxide-based

fairfair PrimerPrimer Polyurethane Polyurethane

PolyurethanePolyurethane GoodGood PrimerPrimer PolyurethanePolyurethane

Polyvinyl Polyvinyl chloridechloride

FairFair Solvent wipe Solvent wipe or primeror primer

Polyurethane, Polyurethane, nitrocellulose nitrocellulose

There are many techniques in painting process:-

◦ Conventional Spray Painting. ◦ Electrostatic painting ◦ Wiping◦ Roller Coating◦ Flow Coating◦ Dip Coating◦ Flocking

It is still one of the more popular techniques for decorating plastics, and today it is being used as much for a functional finish as a decorative finish.

ABS exterior trim and styrene structural foam exterior window shutters, for example, are painted not only for aesthetic purposes but to increase their resistance to UV exposure.

There are a number of different ways to apply paint to plastic.

The most common is conventional spray painting, ranging from the simple hand gun system to highly automated systems with automatic screen washers and elaborate masks for multiple-color decoration.

It should be noted, however, that not all parts are suited to an automated operation by virtue of size

Or because the volume is not large enough to warrant the expenses of such an operations.

In a spray painting system, a key factor is the type of gun used. Various methods are available

Usually two guns mounted so that they rotate around a part to get at hard to reach sports.

It have a back-and-forth action and travel on a curved transverse to paint the sides of complex parts.

In which the parts rotate on a spindle while the guns are stationary (and can paint small part from the top and bottom at the same time).

Like rotating guns and reciprocating parts or rotating parts and reciprocating guns.

Also essential to most spray operations is the use of a mask to shield off those sections of a part which are not meant to be painted.

These form-fitting masks are generally made by electroforming and while they vary considerably in complexity, they usually fall into one of these four categories:-

It is used for painting a depressed name or design.

In this mask a lip of metal extends down the vertical side wall of the depressed design, all the way or only part way down the side wall, depending on the result desired.

This lip must be thin, yet strong. The centers of letters and numbers such as O,A,6,8 must be securely held in place by bridges.

The fit and the lip of the mask ensure a clean sharp paint line.

The draft angle of the depressed design should be at least 5 degrees.

It is the reverse of the lip. It is used where the embossed name or

design is to be kept clean while painting the background.

The lip of metal must cover the vertical side walls all the way to the bottom.

So as to protect the embossing completely.

It is used for protecting a depressed design while painting the background. Its principal use is with transparent articles such as automobile horn buttons and doors of refrigerator evaporators and where vacuum plating is required.

Here again the positive fitting essential to prevent fogging on vertical side walls and bottoms of such designs is accomplished by electroforming directly into the design.

The plugs are cut out, and finished with the proper radii and draft angles to facilitate painting.

They are then suspended by fine wires, usually attached.

In designing molds, the engineer must remember that the draft angles of the depressed design should be kept to a minimum, preferably not more that 5 to 7 degrees.

This type of masking is employed for high production dial filling of letters and numerals, when the width of the groove is less than 3/32" (.093).

This method is frequently employed with sprayed "Wipe-In and "Dry-Wipe" dial filling materials.

When application of a design is required on a flat surface, without recessed or raised lettering,

it is feasible by careful control of the painting operation to use an engraved type mask.

Typical products are balls, scale model trains, and racing cars

Occasionally it is not feasible to cap small letters or numerals, due to size, on a large painted area.

A wiping or highlighting mask is provided that permits the raised surfaces to protrude for secondary wiping or buffing.

The mold engineer should design the mold with thought to the problems of masking. Slight changes in the demarcation of colors which will not essentially change the design of the article may definitely facilitate the masking.

In operating a spray painting set-up, it is important that the masks be washed on a regular basis.

Most set-ups today involve some type of automatic washing system.

To achieve best production efficiency, whether the masks is on or off the machine, three or four masks are often required for each part.

This gives at least one mask on the painting operation, one being washed and one being dried.

Until recently, most masks were washed with solvents.

Government regulations concerning the discharge of solvents into the atmosphere, however has encouraged users to look in other directions.

Typical: cleaning paint masks with water-based materials that are non-toxic nonflammable and lower cost.

In one such system, a water-soluble protective film is applied to the mask surface.

When the mask needs cleaning. It is immersed in hot water or a heated

solution and the protective film dissolves, taking the paint alongwith it.

In essence, the paint is not dissolved, but taken off mechanically.

Another key element in a spray painting operations is the spray booth itself.

Selection of the right type of booth will depend on the plastic being sprayed, the methods of application, and the rate of production desired.

There are three types on the market today:-

The water-wash booth incorporates a continuous waterfall in the back of the booth that literally washes paint out of the exhaust air. It is especially useful in continuous spray production lines.

In a filter booth, a filtering device traps over-spray particles.

It is most suitable for long runs when using slow drying or light viscosity materials or for intermittent or short runs not matter what type of paint is used.

Since filters must be replaced regularly, roll-type dispensing units have been developed.

Battle booths are used where exhaust air to the outside does not have to be free of paint particles.

This type is suitable for intermittent production with quick drying materials.

Baffles assure an even air flow distribution through the work area of the spay booth.

Unsatisfactory results in spray application may be due to a variety of causes, such as faulty technique on the part of the operative, or again, spraying at an incorrect pressure.

In some instances they may arise from failure to keep the gun clean and in good condition; the following are those which occur

This may be due to a dirty or damaged air cap or from the tip not centering properly; to remedy, remove and clean the cap, paying special attention to the air ports.

Should one of these be blocked with dried paint, the shape of the air stream and atomized paint will be irregular.

If any parts are damaged, see that they are replaced.

This may result from too much atomizing pressure or from misalignment of tip and nozzle, or from an obstructed port.

This is probably due to the air valve not seating properly and, provided no actual damage has been sustained by the gun, can be remedied by cleaning.

In this case the needle may not be seating correctly in the fluid tip, due to dirt or other impurities in the tip.

Alternatively, the needle may be bent or of an incorrect size for the tip.

This is probably caused by an air leakage through the needle-packing gland; the trouble can be rectified by means of a new packing washer.

This fault, in which the material is deposited on the surface too dry, as a kind of dust, is usually the result of spraying at too high an air pressure which causes the solvents in the finish to evaporate from the atomized particles before the latter reach the surface.

This may be due to the material itself not possessing sufficient flow or to the use of unsuitable thinners.

Again, it may be caused by the use of too low an air pressure in relation to the viscosity of the material, with the result that atomization is imperfect.

These occur when too much paint is projected on to the surface in any one area, due to incorrect handling of the gun, as when there is too much overlapping in succeeding strokes.

Once the function of the spray plant and a general knowledge of the best uses to which it may be placed are known, the user will be in a position to carry out the various effects which are possible in spray painting.

The scope of the operator will be enlarged considerably and ideas may be carried out which are completely outside the scope of the brush.

The remainder of this chapter will describe how the various designs are to be obtained, and with a little practice and ingenuity many pleasing and effective patterns are obtainable.

In the early 1970’s the government enacted various air pollution laws that restricted the emission of photochemical reactive solvents into the atmosphere.

Included in this classification were the aromatic hydrocarbons like toluene and the branched chain ketones.

As a result, a great deal of effort has been expended on creating water-based coatings that do not involve the use of solvents.

These paints are based resins such as alkyds and acrylics and can be applied by the same methods used for solvent based coatings.

Water-based paints are advantageous for use on plastics because the absence of a solvent eliminates attack on the plastic substrate.

However, such systems are higher in cost than solvent-based coatings and, at this writing, there are still limitations in terms of the system’s failures in humidity or water soak.

Water – base coatings are available today for use on acrylic, ABS, polystyrene, and polycarbonate.

Another development to meet air pollution regulations is the high-solids coatings.

These doe not eliminate solvent emission completely, but greatly reduce the amount of solvent given off.

Coatings based on polyester, epoxies, polyurethanes, and alkyds are available in these formulations.

Because of their high solids content, special equipment is sometimes required for their applications.

One of the newer and more important developments in the painting of plastics is the use of ultraviolet or electron beam radiation to cure the coating (usually based on unsaturated polyesters or acrylics).

These techniques are adaptable to the air pollution law3s described above since the coatings involved contain little or no solvent.

Moreover, they doe not required heat for drying and curing. Curing cycles are virtually instantaneous and the finished coatings show extreme harness and abrasion resistance.

In this set-up, the molded parts are first sanitized for electrostatic painting and a pigmented acrylic monomer coating is then applied by reciprocating electrostatic disc guns.

The coated moldings pass into a concrete enclosed radiation chamber, where a nitrogen atmosphere prevents oxidations and improves color control.

In the curing chambers, the molding pass under twin banks of electron accelerators which polymerize the coatings.

The parts may be stacked immediately after painting. The system is called Electrocure and has been made

available for licensing to other companies.

Radiation is used to crosslink or cure unsaturated organic resins into durable coatings having excellent physical properties with high chemical and temperature resistance.

Type of radiation source, Organic polymer to be irradiated, Mechanisms of physical and chemical

interaction, Final properties associated with the cured

product.

Radiation curing coatings react through unsaturated sites on oligomers and monomers.

These active sites (double bonds) are capable of reacting to form larger and cross linked polymers.

Then, three dimensional network structures are obtained.

a decrease of tack,an increase in cohesive strength,an increase in temperature and chemical resistance.

The exact curing window for a product must be determined for every formulation and for each thickness.

For many radiation curing coatings, the processing window is narrow, making it easy to under-cure or over-cure the coating.

The main sources of energy for curing coatings by radiation are electron beam (EB) and ultraviolet light (UV).

Both provide instantaneous curing of coatings that polymerize from a liquid to a solid when irradiated.

There are a number of painting techniques available to achieve a wood like effect on plastics, particularly when working with structural foam plastics that offer molded – in grains.

A typical system is as follows for achieving a wood grain effect on polystyrene structural foam part:-

The part is first sprayed with a barrier coat to shield the plastic from being attacked by the solvents in subsequent stains and topcoats.

A wiping stain is then sprayed on and wiped with an absorbent cloth to give the basic tone effect.

This stain is force dried so that it will not dissolve when the next glaze is applied.

This subsequent glaze is applied. This subsequent glaze is a toning glaze that is

sprayed eon the part, then brushed into the raised portions to give a complementary dark and light hue within the grained portion.

Finally, a clear topcoat is sprayed over the entire piece to provide gloss and abrasion resistance.

This is considered a four-coat system. Others are available, such as a one-coat system, in which the part is sprayed with stain, then brushed off to achieve the grain effect, then brushed off to achieve the grain effect, or a two coat system in which parts are sprayed with different color barrier coats to achieve a wood-like appearance, then covered with wiping stain to fill in the grain.

One of the newer techniques for painting plastics involves creating an electrical attraction between paint and part so as to minimize overspray and paint waste.

In electrostatic painting the plastic part is first rendered conductive by applying salts such as hygroscopic ionized salt solutions methods of application for this pretreatment can rage from conveyorized dip to rotation of the part on spindles.

The paint and the part are then oppositely charged to create the electrical attraction.

In essence, a high voltage charge is placed eon the paint particles while the part to be painted is grounded.

Because of this attraction, paint that would normally be lost as over- spray in a conventional spray painting operation will wrap around the part and be attracted to the sides and back.

Some systems claim up to 100% paint utilization.

One limitation of electrostatic coating is that it may not lend itself to mask painting.

It is usually most applicable where the entire surface of the part is to be painted.

Typical of the applications that have found use for electrostatic painting are ABS grilles and other automotive parts which incorporate surfaces at many angles from the gun.

In choosing a solvent system for electrostatic painting it is important that the system be formulated to have the proper polarity to wrap around the part and to be slow enough to prevent dry spray in deep recessed areas and on the rear of the part.

One modification of spray painting is the paint-wipe operation.

While there are no clear-cut borders in the selection of paint/wipe vs. mask painting.

Paint/wipe should be seriously considered when dealing with a product where, with a fairly flat surface, a lower surface is to be painted.

The wipe set-up itself is an automatic operation.

Its use is probably more expensive than the cost of a mask, but a much higher volume can be handled, and in some cases, where very fine lettering or design is involved, it is almost impossible to design masks to do the job.

Wiping can be either manual or automatic. However,, unless labour cost is very low, it is rarely feasible to consider manual wipe.

In automatic wipe, product indexes from the paint station to a wipe station where an absorbent fabric-generally a disposable soft paper,

but some processors use a reusable fabric-passes over the top of the product taking paint off the flat surface and leaving the paint in the indented parts. A light solvent spray can be used to aid in paint removal.

Roller coating is just the reverse of wiping. This coats a raised surface of a part, leaving recessed parts free of paint.

No secondary operations are required; the process does not paint lower surfaces even when only slightly raised sections are used.

ROLLER COATING

This is another painting option that involves paint applied from over head nozzles onto racked parts.

The excess coating drains off the parts after painting and is recalculated for use in the next cycle, resulting in very little waste.

The process is not continuous, but many parts can be handled in a single cycle.

In flow coating, part geometry plays a key role, since features like sharp corners could lead to excessive paint build-up.

In this technique, the part is literally dipped into a paint bath, the idea being again to limit waste through overspray.

Automatic systems for raising and lowering parts are used to control the uniformity of the coating thickness.

However, parts that might trap excessive air cannot be dip coated because they will required prolonged drain time.

This decorating technique is also classified as a variation on painting on painting.

In essence, it involves coating a plastic part with adhesive lacquers tinted to match the flock color; then, the flock (i.e. fibers) is applied with a special flock spray gun.

Flock can give a plastic part the appearance and feel of such materials as felt, suede, or short-napped mohair.

A number of techniques are in use today to impart a metallic finish to a plastics part. Hot-stamping can be used to put a gold, silver, or other metallic decoration onto plastics.

More recently, high luster metallized silver foils or roll leaf have been developed for exterior use (e.g. on automotive trim).

Spray plating is another method for giving plastics a metallic surface.

Here, a silver or copper plating is deposited by chemical reaction of water-based solutions on the substrate.

In most cases, the system requires a base coat and a topcoat.

In the system, silver – containing salts are deposited on a product through a dual nozzle gun.

In cases where copper is to be applied, the silver is applied first and the copper is applied over the silver coat.

A typical system would consist of four guns-one for water to clean the part after each processing step, one for the activator to treat the surface of the part, a dual nozzle gun for silver and a dual nozzle gun for copper-a spray booth with a special bottom to recover the silver, mixing vessels an dematerialize for water purification. Automated systems are available on a custom-made basis.

In vacuum deposition, the first step is to jig up the article so that when in the vacuum chamber no part of it will be shielded, and thus fail to be coated.

Jigging is different for every shape and size to be metallized.

Experience, or trial and error, sets the final pattern for jigging. Jigs should be made of metal.

Next, it is usually necessary to lacquer the plastic to provide base sufficiently shiny to give the deposited aluminum a reflective surface.

Only rarely do the shape of the article and the high polish of the mold make this lacquering unnecessary.

The lacquering is done by a dip with slow removal, by spraying, or by dipping and spinning, whichever will best provide a coating free from runs.

The lacquered articles are dried in an oven. All solvents should be removed, since residual solvent will interfere with attaining a vacuum in the chamber.

Chamber ready for fixtures

Parts emerging from chamber

Tooling shop, Designers Metal craft, has been fabricating fixtures for over 40 years and brings a wealth of knowledge to cost effective, tight-tolerance tool making.

With their addition of state-of-the-art equipment such as the Cincinnati CL-6 laser cutting station pictured below, and their Premier computer-controlled precision metal brake, they are able to quickly design and build long-lived tooling to support our metallization process.

Both Mueller Corporation and Designers Metal craft are fully equipped to handle your CAD/CAM digital files in order to accurately develop the best solution for your job.

Custom Fixture Fabrication

CAD/CAM cutting & forming'

Precision Bending

The process begins by loading the parts onto vacuum metalizing holding fixtures that are custom designed for each product, allowing for maximum efficiency both in the number of parts and the handling of the fixture for processing.

The parts are loaded by hand and individually inspected for obvious defects in the raw part and any defect in the holding fixture.

Strict adherence to quality standards assures that no contaminants are picked up in this process.

Custom Holding of Raw Parts

Individual Loading

Custom Fixtures Ready for Loading

When it is required, a water-clear topcoat is applied to enhance abrasion and chemical resistance.

Dye may be added to the topcoat in order to produce a colored metallic finish.

The topcoats are applied in the same manner as our basecoats, High Volume Low Pressure spray guns (HVLP) in either hand-spray, automated spray, or robotic spray booths.

The parts are then ready for the final curing of the topcoat and return to the batch ovens for the last time before inspection.

All work is done in a clean and responsible manner so as to produce the best finish with the least impact on the environment.

Vacuum metalized finishing often includes the application of a specially formulated paint as a basecoat to promote adhesion and to provide a smooth surface, assuring maximum brightness and luster.

Mueller Corporation has developed proprietary coatings for many substrates, including flexible plastics, which are suited for both high and low temperature applications.

All coatings are applied by High Volume Low Pressure spray guns (HVLP) in either hand-spray, automated spray, or robotic spray booth as dictated by the individual requirements of each job. Please enquire as to your specific requirements.

Finished parts are moved to the final inspection and packing area where they are removed from the fixtures and inspected.

All inspection criteria is per each customer’s standard for that individual part, and according to their own requirements, following ISO/TS 16949 & AS 9100 guidelines. Parts are then packed for shipment according to customer’s specifications.

Many People think it’s impossible to chrome plastic, it is not.

While it is possible to electroplate/chrome plate on plastic it is a difficult and expensive process.

Vacuum metalizing is the most common process used for a chrome look on plastic.

Vacuum Metallizing is process used to make, toys, flash light reflectors and automotive trim, shine like chrome.

Vacuum Metalizing DOES NOT have the same durability or corrosive resistance that chrome plating does.

Before parts are metalized they are washed and base coated to ensure a smooth finish to coat over

During the Vacuum Metallizing process aluminum is evaporated in a vacuum chamber, which than condenses back on and bonds to the parts to form a uniform layer, which shines like chrome.

After the metalizing takes place there is a protective topcoat applied similar to the ones used in the automotive industry. You can also add dyes to the topcoat to achieve bright chrome colors gold’s, bronze’s, copper’s, and gunmetal’s.

Chrome vacuum metalizing should not be cleaned with abrasive materials; you should only clean it with a damp soft rag. The chemicals in household cleaners can affect the clear coat casing it to become hazy/milky.

◦ Vacuum Metallizing conforms to the base material that is being coated. If there is texture, scratches, blister, etc it will show through the coating.

It is much more environmentally friendly and cost effective than chrome plating or chrome painting.

You can vacuum metalize many materials including plastic, metal, glass, fiberglass, and more. There are many different applications for Vacuum Metallizing including; automotive and motor sport accessories, automotive interior trim, sporting goods, toys, models, novelty items, display items, decorative fixtures, cosmetic closures, etc.

If you want the look of custom chrome on anything plastic, glass, metal, etc. Mueller Corporation can do the job.

Plastics decorating is emerging as an important technique in plastics processing. The diverse fields of application always call for new techniques and innovative problem solving approaches. Though various decorating techniques have been introduced that complement conventional joining methods, the innovative potential of aesthetic look has yet to be fully exploited. By virtue of its precise and controllable application of this process produces an optically perfect products, which is of crucial importance in the manufacture of decorative components.